Looking for a print or diagram for the AR15 barrel extension; dimensions & tolerance. I could mic one but I'm trying to avoid tolerance stacking and possible errors. A 9mm AR barrel print would be a bonus. Thanks.

This question poped into my head the other day. What are the AR15 Barrel threads? Are they metric? The reason the question poped into my head is a friend was talking about rebarreling his and he was maybe hinting that he wanted me to do it. However, I can not cut metric threads on any of my lathese without buying same more gears. Gary P. Hansen

The barrel extension is 0.9980/0.9995 I think, not near a print right now. The upper receiver bore is 0.999/1.000 for the first inch I think.

If you find a print, it would be most helpful. Trying to determine the od of the rear portion of the extension, the dia of the ring, the distance from the ring face to the breech face. Need this info for a 9mm barrel that is turned from a solid piece of barrel, no barrel extension. TIA

The barrel-shank is .8125-16. I make mine .619" from the shoulder to the end of the shank. Use your threading cutter to cut a chamfer on the outside edge of the shank. You will need a thread-relief groove at the shoulder or the barrel-extension will not thread up to the shoulder. I use .100" groove, and only go the depth of the threads.

Just wanted to revive this thread as I am looking for the same information. I would like to get some barrel extensions manufactured as they are not easy to get here in Canada. Also looking for good, preferably factory, blueprints for the upper receiver.

Just wanted to revive this thread as I am looking for the same information. I would like to get some barrel extensions manufactured as they are not easy to get here in Canada. Also looking for good, preferably factory, blueprints for the upper receiver.

The only prints you will find will be reverse engineered. Colt retains the rights to the AR15 platform & prints. The only time they become available is when the U.S. Gov't puts the weapon manufacture up for bid. You have to be a qualified bidder and sign a NDA to get a copy of the original prints.

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